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2 Microplastics in Freshwater Environments – With Special Focus on the Indian Scenario
Sumi Handique
Department of Environmental Science, Tezpur University, Tezpur, Assam, India
2.1 Introduction
Over the last 50 years, plastic has revolutionized the way we live and is now an essential part of our lives. Globally, plastic wastes have increased at a staggering rate in the last few decades, and around 79% are disposed of in landfills or in the surrounding environment with no proper waste management (Geyer et al. 2017). Out of this, a staggering amount of plastic waste, approximately 4.8–12.7 million tons, is estimated to enter the oceans each year, a large quantity of which comes from land‐based sources and is transported by fluvial or aeolian processes (Jambeck et al. 2015). Rivers are one of the main contributors of plastic waste to the oceans, and are reported to carry 2 million tons of MPs annually (Lebreton et al. 2017). It has been investigated and found that this river‐transported plastic makes up 80% of the plastic debris released from the terrestrial environment to the oceans (Horton et al. 2017; Law & Thompson 2014). With this growing awareness of the importance of the riverine source of plastic wastes in the marine environment in recent years, several studies have been carried out in various world rivers. These include the Los Angeles River (Moore et al. 2005), Danube (Lechner et al. 2014), Yangtze Estuary (Zhao et al. 2014), Rhine (Mani et al. 2015), Selenga River (Battulga et al. 2019), Beijiang River (Tan et al. 2019), Ciwalengke River (Alam et al. 2019), and others. This chapter discusses the various works done with freshwater MPs across the globe, with a special focus on studies in India.
2.2 The Nature and Production of Microplastics
The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) (2015) defines plastic as a synthetic, water‐insoluble polymer, generally of petrochemical origin, that can be molded on heating and designed into various shapes to be maintained during use (Arthur et al. 2009; Lassen et al. 2015).
The plastic pollutants encompass a wide range of synthetic polymers, some of which are polyethylene terephthalate, high‐density polyethene, polyvinyl chloride, polyethene, polypropylene, and polystyrene. These present a wide range of different sizes of plastic polymer materials that are present (meter to micrometers) in our surroundings. According to National Oceanic and Atmospheric Administration (NOAA) and the European Chemicals Agency, MPs are small plastic pieces less than five millimeters.
After entering the ecosystems, these plastic particles undergo degradation and fragmentation processes and it becomes difficult to identify and remove them, particularly the smaller size fractions. These particles are water‐insoluble and not easily biodegradable, and are chemically durable over long periods. These MP pollutants easily move long distances through aeolian transport (Gasperi et al. 2018) and water, and accumulate in the environment. Thus, due to the validation of the long‐range transport of plastics via air and water, the misconception of plastics being a local junk or waste as thought of a few decades ago is now being rebuffed, and plastics are now acknowledged as a serious threat to the global environment.
The threat of plastic pollution can be managed early through efficient source identification. In recent years many researchers have reported potential MP sources, fluxes, and sinks of these pollutants using theoretical models (Figure 2.1) across a wide variety of hydrological reservoirs (Alimi et al. 2018; Browne 2015; de Souza Machado et al. 2018; Horton et al. 2017; Horton & Dixon 2018; Nizzetto et al. 2016; Wagner et al. 2014). Extensive risk management and assessment of this emerging contaminant requires a proper and exhaustive understanding and quantification of the sources and emissions pathways across the world, spatially as well as temporally, with a special focus on freshwater